Weird MegaST issue..

[Bikerbob]

I was doing the A/B mod to this computer, it was screwing up.. and I could not figure it out. I have removed the mod.. completely. I still have the problem.. So its not my mod..

The computer will access an internal drive np..

If I plug a external drive in ( I Have tried 2 drives, two controllers , two cables) when I try and access drive B - external - it will access both A &B - SO my internal drive on this computer is getting both D0SEL and D1SEL - it is trying to read and the head moves just as if I was using drive A - but trying on drive B - Sometimes it will work, other times no.. but this is not supposed to be happening. I have looked over the schematic, the board, and I cannot figure out how this can be happening.

Open to suggestions.

James

[frank.lukas]

Atari floppy disks are always jumped as a drive A (DS0), regardless of whether they are internal or external. So check what have you modify?

[Bikerbob]

Atari floppy disks are always jumped as a drive A (DS0), regardless of whether they are internal or external. So check what have you modify?

Frank, these same drives all work perfectly fine on other machines. I have 8 different ST machines here at the moment. They are Std DD external drives and the internal drives are all SMD-380 (DD) and SMD-340(HD) drives. All jumpered correctly to work in any machine.

This is why this was so frustrating and baffling. I though I had done something wrong with the A/B mod.. in fact there is a problem on the MB causing this. I will try a few different cables.. maybe there is something to that???

James

[frank.lukas]

What have you done/mod on the shugart internal bus ?

[Bikerbob]

Seems like it was a cable.. and I even had 2 of them.. bought them a while back.. seemed like great cables..

cable.jpg (74.43 KiB) Viewed 1771 times

no idea why.. but they look fine, in the package.. new.. but they caused all this. 34pin std ribbon cables work perfect.

James

[rubber_jonnie]

Do the cables have a twist in them? Those are not suitable for the ST.